Resonator, filter, duplexer, and high-frequency circuit apparatus

ABSTRACT

In a resonator having a dielectric member and an electrode formed on the dielectric member, a displacement area (D area) having a high vertical electric field component, and a short or steady area (S area) having a vertical electric field component of zero or close to zero are provided in an interface between the dielectric member and the electrode. A single-layer conductive film divided into portions is formed in the D area or on the side surfaces of the dielectric member, and a multilayer thin-film electrode is formed in the S area or on the end faces of the dielectric member. Conductive thin films of the multilayer thin-film electrode are alternately connected to the single-layer conductive film portions. In-phase currents having the same amplitude flow to the conductive thin films of the multilayer thin-film electrode in the S area in radial direction with respect to the axis of symmetry, thus achieving low-loss operation of the multilayer thin-film electrode in the S area.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a resonator, filter, duplexer,and high-frequency circuit apparatus used in the microwave or millimeterwave band for use in radio communication or in electromagnetic-wavetransmission/reception.

[0003] 2. Description of the Related Art

[0004] In the related art, U.S. Pat. No. 6,148,221 (the '221 patent)discloses a resonator incorporating a multilayer thin-film electrode.

[0005] The multilayer thin-film electrode disclosed in the '221 patentis formed by alternately layering conductive thin films and dielectricthin films, and serves as an electrode which provides low loss in ahigh-frequency region. In a design method disclosed in the publication,the optimum thicknesses of the conductive thin films and the dielectricthin films depend upon the conductivity and the dielectric constant,respectively. Optimizing the thicknesses of the conductive thin filmsand the dielectric thin films allows the current density to be uniformlydistributed over the layered conductive thin films, thereby mitigatingthe skin effect. The multilayer electrode can therefore be operated withlower loss than a single-layer electrode.

[0006] In the resonator disclosed in the '221 patent which incorporatesa multilayer thin-film electrode, the dielectric constant and thicknessof the dielectric thin films are adapted to control a displacementcurrent between the conductive thin films in order to distribute acurrent substantially uniformly over the conductive thin films of themultilayer thin-film electrode. Thus, the following two requirements areessential for low-loss operation of the multilayer thin-film electrode:

[0007] (1) that the multilayer thin-film electrode be orthogonal to theorientation of electric field vector; and

[0008] (2) that the dielectric constant and thickness of the dielectricthin films be designed to be optimum or close to optimum.

[0009] In the resonator disclosed in the '221 patent, therefore, asingle-layer electrode is used for an electrode tangential to theorientation of electric field vector, and ends of each of the thinconductive layers of the multilayer thin-film electrode formed on thesurface orthogonal to the orientation of the electric field vector areshort-circuited by the single-layer electrode. Otherwise, the surfacetangential to the orientation of the electric field vector is open, andno electrode is formed on that surface.

[0010]FIGS. 16A and 16B are a top plan view and a front view,respectively, of an open-circuited circular TM010-mode resonator in therelated art. FIG. 16C is a cross-sectional view showing an enlarged partof the resonator shown in FIG. 16B. In FIGS. 16A to 16C, a multilayerthin-film electrode 10 having a two-layer construction in which adielectric thin film 3 is sandwiched between conductive thin films 2 aand 2 b is formed on each of two parallel surfaces of a cylindricaldielectric member 1.

[0011]FIGS. 17A and 17B are a top plan view and a front view,respectively, of a short-circuited circular TM010-mode resonator. FIG.17C is a cross-sectional view showing an enlarged part of the resonatorshown in FIG. 17B. In FIGS. 17A to 17C, the peripheries of conductivethin films 2 a and 2 b are connected to a single-layer conductive film 4so that the peripheries of the conductive thin films 2 a and 2 b may beshort-circuited.

SUMMARY OF THE INVENTION

[0012] Accordingly, it is an object of the present invention to providea resonator, filter, duplexer, and high-frequency circuit apparatushaving an electrode formed in a region where the vertical electric fieldcomponent is zero or close to zero, whereby the conductor loss of thatelectrode can be reduced, thus achieving low-loss operation.

[0013] In an aspect of the present invention, a resonator includes adielectric member and an electrode formed on the dielectric member. Insuch a dielectric resonator, a displacement area (D area) in which anelectric field has a higher vertical component than a predeterminedthreshold, and a short or steady area (S area) in which an electricfield has a lower vertical component than the threshold are provided inan interface between the dielectric member and the electrode. Theelectrode in the S area comprises a multilayer thin-film electrodeformed by alternately layering conductive thin films and a dielectricthin film. Over the conductive thin films, currents having substantiallyequal amplitude are forcibly excited. The predetermined threshold isclose to zero, and is, for example, about 5% of the maximum electricfield strength in a resonant mode used.

[0014] In the multilayer thin-film electrode in the S area, thedielectric thin film is sandwiched between the upper and lowerconductive thin films, thereby forming a multilayer thin-film electroderesonator.

[0015] In the multilayer thin-film electrode resonator, if theelectrical angle for 5% of the maximum electric field strength isindicated by θ1, then, sin θ1=0.05. That is, the electrical angle θ1 isapproximately 2.87°.

[0016] Integration of displacement currents is expressed by thefollowing equations: $\begin{matrix}{I_{d} = {{\int_{0}^{\pi/2}{\sin \quad \theta {\theta}}} = {\left\lbrack {{- \cos}\quad \theta} \right\rbrack_{0}^{\pi/2} = 1}}} & (1) \\{I_{d1} = {{\int_{0}^{\theta \quad 1}{\sin \quad \theta {\theta}}} = {\left\lbrack {{- \cos}\quad \theta} \right\rbrack_{0}^{\theta \quad 1} = {1 - {\cos \quad {\theta 1}}}}}} & (2)\end{matrix}$

[0017] Substituting θ1 having a value of approximately 2.87° intoEquation (2), then, I_(d1) is approximately 0.00125 (0.125%).Specifically, in a range of the above-noted threshold of 5% of themaximum electric field strength or lower, in the S area, the ratio bywhich an actual current is transformed into a displacement current is0.125% or lower. Therefore, if the distribution of the actual currentwhich is substantially uniformly distributed over the S area is deviatedfrom the sine wave distribution expressed by Equations (1) and (2), theabove ratio is within about 0.125%. Thus, if an actual current istransformed into a displacement current by a small ratio, condition thatthe multilayer thin-film electrode is operated with low loss can besuccessfully reserved. Therefore, a boundary of the S and D areas shouldbe defined using, as a threshold, about 5% of the maximum electric fieldstrength in a resonant mode used.

[0018] A current source in a passive circuit can be regarded as aboundary condition. This means that the current source is connected to aconductor in another passive circuit. For example, in a passive circuitin a multi-conductor mechanism having a high symmetrical structure andhaving an electromagnetic mode that is highly symmetrical, currents areuniformly distributed over the conductors.

[0019] According to the present invention, such conductors are connectedto the conductive thin films of the multilayer thin-film electrode inthe S area in a symmetrical fashion with the conductors, thus achievingforced excitation with uniform current amplitude.

[0020] In a specific form, the electrode in the S area may comprise amultilayer thin-film electrode formed by alternately layering conductivethin films and a dielectric thin film, and the electrode in the D areamay comprise a multilayer thin-film electrode having the same number oflayered films as the number of layered films of the multilayer thin-filmelectrode in the S area, such that the corresponding conductive thinfilms of the multilayer thin-film electrodes in the S area and the Darea are electrically connected to each other.

[0021] This structure allows a current in the conductive thin films inthe D area to be distributed over the conductive thin films of themultilayer thin-film electrode in the S area, thereby causing a currentto substantially uniformly flow to the entire part. As a result, theconductor loss of the multilayer thin-film electrode in the S area canbe reduced.

[0022] In another specific form, the electrode in the S area maycomprise a multilayer thin-film electrode formed by alternately layeringconductive thin films and a dielectric thin film, and the electrode inthe D area may comprise an electrode which is divided into substantiallycongruent electrode patterns of an integer multiple of the number ofconductive thin films of the multilayer thin-film electrode in the Sarea, such that the electrode patterns and the conductive thin films ofthe multilayer thin-film electrode in the S area are connected to eachother correspondingly.

[0023] This structure allows a current in the separated electrodepatterns in the D area to be distributed over the conductive thin filmsof the multilayer thin-film electrode in the S area, thereby causing acurrent to substantially uniformly flow to the entire part. As a result,the conductor loss of the multilayer thin-film electrode in the S areacan be reduced.

[0024] The resonator according to the present invention may use adielectric member having one or a plurality of curves and a plurality offlat surfaces, or a dielectric member having a plurality of flatsurfaces, in which the D area and the S area are defined in each of thesurfaces of the dielectric member.

[0025] This makes it easy to form a multilayer thin-film electrode oneach surface of the dielectric member or to form a plurality ofseparated electrode patterns.

[0026] In the resonator according to the present invention, preferably,the thickness of at least one of the conductive thin films is 2.75 timesthe skin depth or lower. Thus, the ratio of the conductive thin films toa bulk conductor in surface resistance can be small, thereby increasingan effect of reducing the conductor loss involved with a multilayerthin-film structure.

[0027] In another aspect of the present invention, a filter according tothe present invention includes a resonator having the above-describedstructure, and signal input/output units. Therefore, a compact filterhaving low insertion loss can be achieved.

[0028] In still another aspect of the present invention, a duplexeraccording to the present invention includes two filters having theabove-described structure. The signal input/output units include atransmission-signal input terminal, a shared transmission and receptioninput and output terminal, and a received-signal output terminal.Therefore, a compact duplexer having low insertion loss can be achieved.

[0029] In still another aspect of the present invention, ahigh-frequency circuit apparatus according to the present inventionincludes the above-described resonator, filter, or duplexer. Therefore,a compact and low-loss high-frequency circuit can be achieved. Acommunication apparatus incorporating such a high-frequency circuit canimprove the communication quality such as a noise characteristic and thetransmission speed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIGS. 1A and 1B are views of a resonator according to a firstembodiment of the present invention;

[0031]FIGS. 2A and 2B are cross-sectional views of the resonator, takenalong lines A-A and B-B of FIGS. 1A and 1B, respectively;

[0032]FIGS. 2C and 2D are cross-sectional views of the enlarged versionof part C and D of the resonator shown in FIGS. 2A and 2B, respectively;

[0033]FIGS. 3A to 3C are views showing the configuration of film layersof a multilayer thin-film electrode in an S area of the resonator;

[0034]FIGS. 4A to 4D are views of a resonator according to a secondembodiment of the present invention;

[0035]FIGS. 5A to 5C are views of a resonator according to a thirdembodiment of the present invention;

[0036]FIGS. 6A and 6B are cross-sectional views of the resonator, takenalong lines A-A and B-B of FIG. 5A, respectively;

[0037]FIGS. 6C and 6D are cross-sectional views of the enlarged versionof part C and D shown in FIGS. 6A and 6B, respectively;

[0038]FIGS. 7A to 7D are views of a resonator according to a fourthembodiment of the present invention;

[0039]FIG. 8 is an equivalent circuit diagram of a filter according to afifth embodiment of the present invention;

[0040]FIG. 9 is a block diagram of a duplexer according to a sixthembodiment of the present invention;

[0041]FIG. 10 is a block diagram of a communication apparatus accordingto a seventh embodiment of the present invention;

[0042]FIGS. 11A and 11B are views for illustrating the operation of amultilayer thin-film electrode with use of forced currents;

[0043]FIGS. 12A and 12B are diagrams of an analytic model of themultilayer thin-film electrode shown in FIG. 11A;

[0044]FIGS. 13A and 13B are graphs showing analysis of the dependencyupon the dielectric film thickness in the multilayer thin-filmelectrode;

[0045]FIGS. 14A and 14B are graphs showing analysis of the dependencyupon the conductive film thickness in the multilayer thin-filmelectrode;

[0046]FIG. 15 is a graph showing the relationship between the conductivefilm thickness and the normalized surface resistance;

[0047]FIGS. 16A to 16C are views of a resonator in the related art; and

[0048]FIGS. 17A to 17C are views of a resonator in the related art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] A resonator according to a first embodiment of the presentinvention is now described with reference to FIGS. 1A to 3C and FIGS.11A to 15.

[0050]FIGS. 1A and 1B are a front view and a right side view,respectively, of the resonator of the present invention. FIGS. 2A and 2Bare cross-sectional views of the resonator, taken along lines A-A andB-B of FIG. 1B, respectively. FIGS. 2C and 2D are cross-sectional viewsof the enlarged version of part C and D of the resonator shown in FIGS.2A and 2B, respectively.

[0051] The resonator is formed of a dielectric member 1 andpredetermined electrodes formed on the dielectric member 1. Thedielectric member 1 preferably has an octagonal tubular shape in which ahole 5, which is preferably octagonal in cross section, is formed in thecenter. A single-layer conductive film 4 is formed on each of the eightside surfaces of the dielectric member 1 so as to be separated at ridgesof the eight side surfaces. The single-layer conductive film 4 is alsoformed on each of the eight inner surfaces of the hole 5 so as to beseparated at comers of the eight surfaces. A multilayer thin-filmelectrode 10 is formed on each of the two parallel end faces of thedielectric member 1.

[0052]FIGS. 3A to 3C show the configuration of film layers of themultilayer thin-film electrode 10. FIG. 3A shows a pattern of a firstconductive thin film 2 a formed on a surface of the dielectric member 1;FIG. 3B shows a pattern of a dielectric thin film 3 which overlies thefirst conductive thin film 2 a; and FIG. 3C shows a pattern of a secondconductive thin film 2 b which overlies the dielectric thin film 3. Asshown in FIGS. 3A to 3C and FIGS. 2C and 2D, the first conductive thinfilm 2 a is electrically connected to four outer surfaces of thedielectric member 1 and four inner surfaces of the hole 5. Also, thesecond conductive thin film 2 b is electrically connected to four outersurfaces of the dielectric member 1 and four inner surfaces of the hole5. It is noted that the first conductive thin film 2 a and the secondconductive thin film 2 b are electrically connected to the single-layerconductive film 4 in an alternate manner, so that the first and secondconductive thin films 2 a and 2 b are electrically isolated from eachother.

[0053] The resonator according to the first embodiment is a coaxialresonator which is resonated in a TEM mode in which the electric fieldvector is oriented between the single-layer conductive film 4 formed onthe inner surfaces of the hole 5 and the single-layer conductive film 4formed on the outer surfaces of the dielectric member 1. A resonatorprovided with the multilayer thin-film electrode 10 on each of the twoparallel end faces of the dielectric member 1 would serve as ashort-ended half wave resonator and a resonator provided with themultilayer thin-film electrode 10 on one of the end faces would serve asa quarter wave resonator. The outer surfaces of the dielectric member 1and the inner surfaces of the hole 5 are herein referred to as a “D(Displacement) area,” and the end faces of the dielectric member 1 onwhich the multilayer thin-film electrode 10 is formed are hereinreferred to as an “S (Short or Steady) area.” The multilayer thin-filmelectrode 10 is formed in the S area, while the single-layer conductivefilm 4 which is divided into two portions, i.e., equal to the number ofconductive thin films (2 a and 2 b in this example) of the multilayerthin-film electrode 10, is formed in the D area, thus allowing in-phasecurrents having the same amplitude to flow to the first and secondconductive thin films 2 a and 2 b in the S area in radial direction withrespect to the axis of symmetry.

[0054] The operation of the multilayer thin-film electrode 10 and thelow-loss effect thereof are now described with reference to FIGS. 11A to15.

[0055]FIG. 11A shows a single-layer conductive film used as a referencemodel and a multilayer thin-film electrode, which has two-layerconstruction, used as a comparative model. FIG. 11B is a graph showingthe ratio of current flow in a first conductive thin film to a secondconductive thin film of the comparative multilayer thin-film electrodeversus the conductor Q. This graph depicts analysis of conductor losscaused by a forced current in a parallel plate line having upper andlower electric walls and left and right magnetic walls. This analysis isperformed using a method in which no displacement current is assumed,but only eddy currents are taken into account. This method is useful foranalysis of a portion where an electric field does not have a verticalcomponent on an interface of a conductive film. As shown in FIG. 11B,the analysis shows that the conductor Q increases by a factor of up to1.51 when a current forces the first and second conductive thin films tobe excited at an amplitude ratio of 1:1.

[0056]FIGS. 12A and 12B show an analytic model of the comparativemultilayer thin-film electrode shown in FIG. 11A. In FIGS. 12A and 12B,this electrode is regarded as a parallel plate waveguide.

[0057]FIGS. 13A and 13B are graphs showing analysis of the dependency ofthe conductor Q upon the dielectric thin film thickness when theparameters shown in FIGS. 12A and 12B are set as follows: <referencemodel> <comparative model> dimension: d₁ = 10 μm d1 = 10 μm h = 60 μm d2= variab1e H = h + d₁ = 70 μm d3 = 1.26 μm h = 60 μm − (d2 = d3) (H =h + d₁ + d₂ + d₃ = 70 μm) current: I₁ = 1A I₁ = 0.5 A I₂ = 0.5 A

[0058] An analytic solution Q_(c) of the conductor Q of the referencesingle-layer conductive film is determined as follows:

Q _(c)=(2h/δ)=(2×60 μm)/1.55 μm=77.4

[0059]FIG. 13A shows the conductor Q expressed as an absolute magnitude,and FIG. 13B shows the normalized version of the comparative model withrespect to the reference model. As shown, when the thickness d₂ of thedielectric thin film in the comparative model changes, the conductor Qvaries moderately, and a conductor-Q increasing factor of one or more isexhibited. When the thickness d₂ of the dielectric thin film is about 10μm, the conductor Q is reduced because the proportion of the thicknessd₂ of the dielectric thin film to the thickness of the substrate in thereference model increases.

[0060]FIGS. 14A and 14B are graphs showing the results of analysis ofthe dependency of the multilayer thin-film electrode upon the conductivethin film thickness. FIG. 14A shows the conductor Q versus the thicknessof the conductive thin film; and FIG. 14B shows the normalized versionof FIG. 14A with respect to the reference model.

[0061] When the thickness d₃ of the conductive thin film in thecomparative model changes, the conductor Q exhibits a sharp peak, and aconductor-Q increasing factor of one or more is exhibited. When thethickness d₃ of the conductive thin film is about 10 μm, the conductor Qis reduced. The reason for this reduction is thought to be that, whenthe first conductive film (a film having the thickness d₃) on theinterface side in the comparative model has a thickness of about 10 μm,reverse currents flow in opposing sides of the first conductive film,thus increasing the conductor loss. The thicknesses of the conductivethin films should be designed so that an area having a high conductor Qcan be used.

[0062]FIG. 15 is a graph showing the relationship between the normalizedvalue (normalized conductive film thickness) obtained by dividing thedistance x from the conductor surface by skin depth δ, and a normalizedvalue obtained by dividing the surface resistance R of a conductive filmby the surface resistance R_(s) of a bulk conductor.

[0063] The relationship shown in FIG. 15 is determined as follows:

[0064] First, an incidence matrix (F-matrix) for a plane wavepropagating in a conductor is expressed by Equation (3): $\begin{matrix}{F = \begin{pmatrix}{\cosh \quad \gamma \quad x} & {Z_{x}\sinh \quad \gamma \quad x} \\{\frac{1}{Zs}\sinh \quad \gamma \quad x} & {\cosh \quad \gamma \quad x}\end{pmatrix}} & (3)\end{matrix}$

[0065] where x denotes the distance from the conductor surface, γdenotes a propagation coefficient, and Z_(s) denotes the characteristicimpedance. The propagation coefficient γ is determined as follows:$\begin{matrix}{\gamma = \frac{1 + j}{\delta}} & (4)\end{matrix}$

[0066] The characteristic impedance Z_(s) is determined as follows:

Z _(s)=(1+j)·R _(s)  (5)

[0067] where δ denotes the skin depth of a bulk conductor, and R_(s)denotes the surface resistance of the bulk conductor.

[0068] The surface impedance of a conductive thin film having thicknessx is calculated by the following equation using the ratio of the 11component to the 21 component of the F-matrix on condition that the backsurface is open: $\begin{matrix}{Z = {Z_{s} \cdot \frac{\cosh \quad \gamma \quad x}{\sinh \quad \gamma \quad x}}} & (6)\end{matrix}$

[0069] Substituting Equations (4) and (5) into Equation (6) andorganizing the resulting equation in terms of the real part and theimaginary part yield Equation (7): $\begin{matrix}{Z = {{R_{s} \cdot \frac{{{\sinh \left( \frac{x}{\delta} \right)} \cdot {\cosh \left( \frac{x}{\delta} \right)}} + {{\sin \left( \frac{x}{\delta} \right)} \cdot {\cos \left( \frac{x}{\delta} \right)}}}{{\cosh^{2}\left( \frac{x}{\delta} \right)} - {\cos^{2}\left( \frac{x}{\delta} \right)}}} + {j\quad {R_{s} \cdot \frac{{{\sinh \left( \frac{x}{\delta} \right)} \cdot {\cosh \left( \frac{x}{\delta} \right)}} - {{\sin \left( \frac{x}{\delta} \right)} \cdot {\cos \left( \frac{x}{\delta} \right)}}}{{\cosh^{2}\left( \frac{x}{\delta} \right)} - {\cos^{2}\left( \frac{x}{\delta} \right)}}}}}} & (7)\end{matrix}$

[0070] The surface resistance is determined from the real part (theimaginary part indicates the surface reactance) as follows:$\begin{matrix}{R = {R_{s} \cdot \frac{{{\sinh \left( \frac{x}{\delta} \right)} \cdot {\cosh \left( \frac{x}{\delta} \right)}} + {{\sin \left( \frac{x}{\delta} \right)} \cdot {\cos \left( \frac{x}{\delta} \right)}}}{{\cosh^{2}\left( \frac{x}{\delta} \right)} - {\cos^{2}\left( \frac{x}{\delta} \right)}}}} & (8)\end{matrix}$

[0071]FIG. 15 shows Equation (8).

[0072] A region shown in FIG. 15 which has an R/R_(s) ratio of one orlower is an area having a smaller surface resistance than that of thebulk conductor. In other words, a multilayer thin-film structure formedon an area having a range of about 1.1417 to 2.7505 times the skin depthachieves an effect of improving the conductor Q. If the thickness x isreduced, the lower limit (1.1417 in FIG. 15) of the normalizedconductive film thickness when the R/R_(s) ratio is one or more isreduced as the number of layered films increases. The value of x/δ(1.5708 in FIG. 15) when the R/R_(s) ratio is minimized also variesdepending upon the number of layered films. The upper limit (2.7505 inFIG. 15) of the normalized conductive film thickness when the R/R_(s)ratio is one or more is constant regardless of the number of layeredfilms. Therefore, the thickness x of the conductive thin film should beselected, depending upon the number of layered films, from a range ofvalues when the value of x/δ is about 2.75 or more.

[0073] Although the multilayer thin-film electrode 10 on the sidesurface has a two-layer construction in FIGS. 1A to 3C, the presentinvention is not limited to this form. A multilayer thin-film electrodehaving three or more conductive thin films may be used, in which caselower-loss operation can be achieved.

[0074] For example, an electrode having four conductive thin films mayalso use a dielectric member having an octagonal cylinder, such that theconductive thin films are electrically connected with four pairs ofsingle-layer conductive films, each pair being formed on two parallelfacing sides.

[0075] According to the first embodiment, thereof, in an electrodehaving three or more conductive thin films, currents having equalamplitudes flow in the conductive thin films, thereby making it possibleto maximize the Q factor of the multilayer thin-film electrode.

[0076] A resonator according to a second embodiment of the presentinvention is now described with reference to FIGS. 4A to 4D.

[0077] The resonator according to the second embodiment is a coaxialresonator having a tubular dielectric member. FIGS. 4A and 4B are afront view and a right side view of the resonator, respectively; FIG. 4Cis a cross-sectional view of the resonator, taken along a line A-A ofFIG. 4B; and FIG. 4D is a cross-sectional view of the enlarged versionof part D of the resonator shown in FIG. 4C. A multilayer thin-filmelectrode constructed by laminating a conductive thin film 2 c, adielectric thin film 3 a, and a conductive thin film 2 d is formed onthe outer surface of the tubular dielectric member 1 and the innersurface of a hole 5. A multilayer thin-film electrode is constructed bylaminating a conductive thin film 2 a, a dielectric thin film 3 b, and aconductive thin film 2 b on each of the two parallel end faces of thedielectric member 1.

[0078] The multilayer thin-film electrode formed in the D area, i.e., oneach of the outer surfaces of the dielectric member 1 and the innersurface of the hole 5, is electrically connected to the multilayerthin-film electrode formed in the S area, i.e., on each of the parallelend faces of the dielectric member 1, through their correspondingconductive thin films. Specifically, the conductive thin films 2 a and 2c are connected to each other, and the conductive thin films 2 b and 2 dare connected to each other.

[0079] In this structure, a resonator provided with the multilayerthin-film electrode on each of the two parallel end faces of thedielectric member 1 would serve as a short-ended half wave resonator;and a resonator provided with the multilayer thin-film electrode on oneof the end faces would serve as a quarter wave resonator.

[0080] A TEM-mode electric field component vertically enters themultilayer thin-film electrode in the D area, thus causing an electricfield to be generated in the dielectric thin film thereof in thethickness direction thereof. This is a displacement current in thedielectric thin film, into which actual currents flowing in theconductive thin films 2 c and 2 d are transformed. The thicknesses ofthe conductive thin films 2 c and 2 d and the dielectric thin film 3 aof the multilayer thin-film electrode in the D area are determinedaccording to a film-thickness design of the multilayer thin-filmelectrode. Specifically, the thicknesses of the conductive thin films 2c and 2 d are designed based on the skin depth and the number of layeredconductive films. The thickness of the dielectric thin film 3 a isdetermined based on the ratio of dielectric constant of the basedielectric member 1 to the dielectric constant of the dielectric thinfilm 3 a, and the number of layered dielectric films.

[0081] In the dielectric thin film 3 b of the multilayer thin-filmelectrode in the S area, no electric field is generated in the thicknessdirection thereof, resulting in no displacement current. Thedistribution ratio in amplitude and phase of the actual currents in theconductive thin films 2 a and 2 b is thus reserved. Therefore, theactual currents in the conductive thin films 2 c and 2 d can besubstantially uniformly distributed in both amplitude and phase. Thisenables low-loss operation in the multilayer thin-film electrode in theS area, as described above.

[0082] As described with reference to FIGS. 13A and 13B, the dielectricthin film 3 b of the multilayer thin-film electrode in the S area doesnot exhibit a sharp peak in a graph of conductor Q versus dielectricthin film thickness. That is, the thickness of the dielectric thin film3 b of the multilayer thin-film electrode in the S area does not have acenter design value. Therefore, the dielectric thin film 3 b should bedesigned to be insulating and to be as thin as possible.

[0083] A resonator according to a third embodiment of the presentinvention is now described with reference to FIGS. 5A to 6D.

[0084]FIGS. 5A and 5B are a top plan view and a front view of theresonator, and FIG. 5C is an enlarged view of part C of the resonatorshown in FIG. 5B. FIGS. 6A and 6B are cross-sectional views of theresonator, taken along lines A-A and B-B of FIG. 5A, respectively. FIGS.6C and 6D are cross-sectional views of the enlarged version of part Cand D shown in FIGS. 6A and 6B, respectively.

[0085] The resonator according to the third embodiment uses a dielectricmember 1 having an octagonal cylindrical shape, and a multilayerthin-film electrode formed of a conductive thin film 2 a, a dielectricthin film 3, and a conductive thin film 2 b is formed on each of theeight side surfaces of the dielectric member 1. A single-layerconductive film that is divided into eight portions 4 a and 4 b by slits6 interposed between the film portions 4 a and 4 b is formed on each ofthe upper and lower parallel surfaces of the dielectric member 1. Theconductive thin films 2 a of the multilayer thin-film electrodes on theside surfaces of the dielectric member 1 are connected to thesingle-layer conductive film portions 4 a formed on the upper and lowersurfaces. The conductive thin films 2 b of the multilayer thin-filmelectrodes are connected to the single-layer conductive film portions 4b formed on the upper and lower surfaces.

[0086] The resonator according to the third embodiment serves as ashort-circuited TM-mode (axially symmetric mode) resonator. An axiallysymmetric mode allows a current to be uniformly distributed over theeight single-layer conductive film portions 4 a and 4 b which areseparated by the slits 6. When a current outwardly flows onto the uppersurface of the dielectric member 1, a current inwardly flows onto thelower surface of the dielectric member 1. As a result, the conductivethin films 2 a and 2 b of the multilayer thin-film electrodes on theside surfaces are forcibly excited with substantially in-phase currentshaving substantially equal amplitude. Since the eight side surfaces ofthe dielectric member 1 are short-circuited, no electric field isgenerated in the dielectric thin films 3 on the side surfaces in thethickness thereof. That is, no displacement current occurs. Thedistribution ratio in amplitude and phase of the actual current in theconductive thin films 2 a and 2 b is thus reserved. As described above,since the thickness of the dielectric thin film 3 does not have a centerdesign value, it is only required that the dielectric thin film 3 beinsulating and that the dielectric thin film 3 be designed to be as thinas a predetermined insulating capability can be given.

[0087] Although the dielectric member 1 which has an octagonalcylindrical shape has been described with reference to FIGS. 5A to 5C,the shape of the dielectric member 1 is not limited to an octagonalcylindrical shape, and any shape may be used. In general, however, apolygonal shape having a larger number of sides is preferred because itcan achieve more ideal current distribution in the multilayer thin-filmelectrode on the side surfaces of the dielectric member 1.

[0088] In FIGS. 5A to 5C, the multilayer thin-film electrode on the sidesurfaces of the dielectric member 1 has a two-layer construction.However, the present invention is not limited to this form, and amultilayer thin-film electrode having three or more conductive thinfilms may be used, in which case lower-loss operation can be achieved.

[0089] A resonator according to a fourth embodiment of the presentinvention is now described with reference to FIGS. 7A to 7D.

[0090]FIGS. 7A and 7B are a top plan view and a front view of theresonator; FIG. 7C is a cross-sectional view of the resonator, takenalong a line A-A of FIG. 7A; and FIG. 7D is a cross-sectional viewshowing the enlarged version of part D shown in FIG. 7C. The resonatoris provided with a multilayer thin-film electrode on each of the upperand lower surfaces and the side surfaces of a cylindrical dielectricmember 1. The thicknesses of conductive thin films 2 c and 2 d and adielectric thin film 3 a of the multilayer thin-film electrode on eachof the upper and lower surfaces are determined according to a multilayerthin-film electrode design. The thicknesses of conductive thin films 2 aand 2 b of the multilayer thin-film electrode on the side surfaces aredetermined according to a multilayer thin-film electrode design. Thethickness of a dielectric thin film 3 b of the multilayer thin-filmelectrode on the side surfaces is designed so as to be insulating and tobe as thin as possible, as in the aforementioned embodiments. Theconductive thin films 2 a and 2 b in the S area, i.e., on the sidesurfaces, are electrically connected with the conductive thin films 2 cand 2 d in the D area, i.e., on each of the upper and lower surfaces, atthe boundaries thereof, respectively.

[0091] The resonator in FIGS. 7A to 7D serves as a short-circuitedTM-mode (axially symmetric mode) resonator. Specifically, an electricfield component vertically enters the multilayer thin-film electrode oneach of the upper and lower surfaces, thus causing an electric field tobe generated in the dielectric thin film 3 a in the thickness directionthereof. This is a displacement current in the dielectric thin film 3 a,into which actual currents flowing in the conductive thin films 2 c and2 d are transformed. The thicknesses of the conductive thin films 2 cand 2 d and the dielectric thin film 3 a of the multilayer thin-filmelectrode in the D area are determined according to a film-thicknessdesign of the multilayer thin-film electrode. The thickness of thedielectric thin film 3 a which is determined according to a multilayerthin-film design, thus allowing the actual currents in the conductivethin films 2 c and 2 d to be substantially uniformly distributed both inamplitude and phase. This causes the conductive thin films 2 a and 2 bin the S area to be forcibly excited with substantially in-phase andsubstantially equal current amplitude. Since the S area on the sidesurfaces are short-circuited, no electric field is generated in thedielectric thin film 3 b of the multilayer thin-film electrode in the Sarea in the thickness direction thereof, resulting in no displacementcurrent. The distribution ratio in amplitude and phase of currents inthe conductive thin films 2 c and 2 d of the multilayer thin-filmelectrode in the D area is thus reserved for the conductive thin films 2a and 2 b of the multilayer thin-film electrode in the S area.

[0092] Therefore, low-loss operation of the multilayer thin-filmelectrodes in the D and S areas can be achieved.

[0093] In the foregoing embodiments, conductive thin films anddielectric thin films are alternately layered to form a multilayerthin-film electrode. However, the multilayer thin-film electrode may beformed by any other technique such as by inserting several tensnanometers of thin-film material, such as titanium (Ti), between theconductive thin films and the dielectric thin films in order to improvethe tightness between the conductive thin films and the dielectric thinfilms.

[0094] A filter according to a fifth embodiment of the present inventionis now described with reference to FIG. 8. In FIG. 8, three resonatorsare implemented by any of the resonators according to the first tofourth embodiments. The resonators are capacitively coupled to eachother, as shown by capacitors in FIG. 8, and the first resonator and thelast resonator are capacitively coupled to input and output terminals,respectively, thereby achieving a three-resonator filter having aband-pass filtering characteristic.

[0095] A duplexer according to a sixth embodiment of the presentinvention is now described with reference to FIG. 9.

[0096] A transmission filter and a reception filter are implemented bythe filter shown in FIG. 8, etc. The filtering characteristics of thetransmission filter and the reception filter should be determined sothat the transmission filter allows a component to pass the transmissionband and the reception filter allows a component to pass the receptionband.

[0097] A phase control is performed between the output port of thetransmission filter and the input port of the reception filter in orderto prevent a transmission signal from being passed towards the receptionfilter and a received signal from being passed towards the transmissionfilter.

[0098] A communication apparatus according to a seventh embodiment ofthe present invention is now described with reference to FIG. 10.

[0099] A duplexer is implemented as the duplexer shown in FIG. 9. Thetransmission terminal and reception terminal of the duplexer areconnected to a transmitting circuit and a receiving circuit,respectively. The antenna terminal is connected to an antenna.

[0100] Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

What is claimed is:
 1. A resonator comprising: a dielectric member; andan electrode formed on the dielectric member, the electrode having: afirst multilayer thin-film portion formed from alternately layeredconductive thin films and a dielectric thin film, the first multilayerthin-film portion having a displacement area provided in a firstinterface between the dielectric member and the electrode in which afirst electric field has a higher vertical component than apredetermined threshold, and a second multilayer thin-film portionformed from the same number of layered films as the first multilayerthin-film portion, the second multilayer thin-film portion having asteady area provided in a second interface between the dielectric memberand the electrode in which a second electric field has a lower verticalcomponent than the predetermined threshold, wherein the correspondingconductive thin films of the first multilayer thin-film portion and thesecond multilayer thin-film portion are electrically connected to eachother.
 2. A resonator comprising: a dielectric member; and an electrodeformed on the dielectric member, the electrode having: a first portionformed from a plurality of electrode patterns, the first portiondefining a displacement area in a first interface between the dielectricmember and the electrode in which a first electric field has a highervertical component than a predetermined threshold so that a displacementcurrent flow is substantially uniform over the first interface, and asecond portion formed from alternately layered conductive thin films anda dielectric thin film, the second portion having a steady area providedin a second interface between the dielectric member and the electrode inwhich a second electric field has a lower vertical component than thepredetermined threshold, wherein the plurality of electrode patterns ofthe first portion and the conductive thin films of the second portionare respectively connected to each other.
 3. A resonator comprising: adielectric member; and an electrode formed on the dielectric member, theelectrode having: a first portion formed from alternately layeredconductive thin films and a dielectric thin film, the first portionhaving a steady area provided in a first interface between thedielectric member and the electrode in which a first electric field hasa lower vertical component than a predetermined threshold, and a secondportion formed from an electrode pattern which is divided intosubstantially congruent electrode patterns of an integer multiple of thenumber of conductive thin films of the first portion, the second portiondefining a displacement area in a second interface between thedielectric member and the electrode in which a second electric field hasa higher vertical component than the predetermined threshold, whereinthe electrode patterns of the second portion and the conductive thinfilms of the first portion are respectively connected to each other. 4.The resonator according to claim 1, wherein the dielectric memberincludes one of a plurality of curves and a plurality of flat surfaces,and a plurality of flat surfaces, and wherein the displacement area andthe steady area are defined in each of the surfaces of the dielectricmember.
 5. The resonator according to claim 1, wherein the thickness ofat least one of the conductive thin films is 2.75 times a skin depth orlower.
 6. A filter comprising: the resonator according to claim 1; andsignal input and output units connected to the resonator.
 7. A duplexercomprising two of the filters according to claim 6, wherein the signalinput and output units include a transmission-signal input terminal, ashared transmission and reception input and output terminal, and areceived-signal output terminal.
 8. A high-frequency circuit apparatuscomprising the resonator according to claim
 1. 9. The resonatoraccording to claim 2, wherein the dielectric member includes one of aplurality of curves and a plurality of flat surfaces, and a plurality offlat surfaces, and wherein the displacement area and the steady area aredefined in each of the surfaces of the dielectric member.
 10. Theresonator according to claim 3, wherein the dielectric member includesone of a plurality of curves and a plurality of flat surfaces, and aplurality of flat surfaces, and wherein the displacement area and thesteady area are defined in each of the surfaces of the dielectricmember.
 11. The resonator according to claim 2, wherein the thickness ofat least one of the conductive thin films is 2.75 times a skin depth orlower.
 12. The resonator according to claim 3, wherein the thickness ofat least one of the conductive thin films is 2.75 times a skin depth orlower.
 13. A filter comprising: the resonator according to claim 2; andsignal input and output units connected to the resonator.
 14. A duplexercomprising two of the filters according to claim 13, wherein the signalinput and output units include a transmission-signal input terminal, ashared transmission and reception input and output terminal, and areceived-signal output terminal.
 15. A filter comprising: the resonatoraccording to claim 3; and signal input and output units connected to theresonator.
 16. A duplexer comprising two of the filters according toclaim 15, wherein the signal input and output units include atransmission-signal input terminal, a shared transmission and receptioninput and output terminal, and a received-signal output terminal.
 17. Ahigh-frequency circuit apparatus comprising the resonator according toclaim
 2. 18. A high-frequency circuit apparatus comprising the resonatoraccording to claim 3.